Our long-term objective is to prevent and/or treat acute renal failure. We showed that activation of the gene for the p21 cyclin-dependent kinase (cdk) inhibitor ameliorated renal failure after cisplatin administration and renal ischemia/reperfusion. After these injuries, comparing p21(+/+) with p21(-/-) mice, there was significantly less cellular damage, including both necrosis and apoptosis, less functional kidney failure, and less mortality in the p21(+/+) population. The mechanism was directly dependent on the role of p21 as a regulator of the cell cycle. We now find that induction of p21 using an adenoviral vector before cisplatin exposure completely protected mouse kidney proximal tubule cells in vitro from cytotoxicity. Similarly, pretreatment of kidney cells with different pharmacologic cdk2 inhibitors or with a histone deacetylase (HDAC) inhibitor known to induce p21 was also protective. We extended these findings by showing that a cdk2 inhibitory drug, with a spectrum of activity similar to p21, also protected kidney function and cell morphology in vivo from cisplatin-induced renal injury. We hypothesize that cdk2 inhibitors protect kidney cells from cisplatin-induced toxicity by inhibiting cell death pathways activated by cisplatin exposure. Furthermore, we hypothesize that cdk2 inhibitors will be useful to prevent and treat acute renal failure. We have developed aims that will determine the mechanism of cdk inhibitor protection in vitro and in vivo and provide initial steps to utilize cdk inhibitors to ameliorate cisplatin-induced renal failure. Our first specific aim is to determine the mechanism of cdk inhibitor protection. We will confirm that cdk inhibitor protection is dependent on repressing cdk2 activity. We will determine cdk2 localization and the localization of cdk2-p21 interaction. We will determine the cell death pathway(s) inhibited by cdk2 inhibitors, and for each death pathway inhibited by cdk2 inhibitors, determine whether it is activated by cisplatin. Our second specific aim is to determine conditions and mechanisms of protection by cdk2 inhibitors in vivo. We will determine whether cdk2 knock-out mice are protected from cisplatin nephrotoxicity, and whether the samefragment of p21 that protects in vitro also protects in vivo. We will confirm purvalanol in vivo protection and refine the conditions for its action.